Drilling apparatus

ABSTRACT

A drilling apparatus for drilling a deviated bore comprising a tubular outer member having an offset and adapted for rotatably supporting a drill bit. The member has a gripping arrangement for selectively engaging the wall of a bore to restrain the member against rotation. An inner member is provided within the outer member for coupling to the drill bit at one end and to a drill string at another end. The apparatus has a first configuration in which the gripping arrangement is retracted and the inner member is coupled to the outer member such that rotation of the drill string provides for corresponding rotation of the inner and outer members, and a second configuration in which the gripping arrangement is extended and the inner member is rotatable relative to the outer member such that the outer member is restrained from rotation in the bore and rotation of the drill string provides for corresponding rotation of the inner member and the drill bit.

FIELD OF INVENTION

The present invention relates to a drilling apparatus, and in particularto a drilling apparatus for drilling deviated bores, particularly, butnot exclusively, for intersecting a subterranean hydrocarbon formation.

BACKGROUND OF INVENTION

In the oil and gas extraction industry, hydrocarbons are extracted froma subterranean formation through bores which are drilled from surfacelevel to intersect the formation. In many circumstances, a number ofvertical bores are required for efficient and effective extraction ofhydrocarbons from a single formation, which often necessitates acorresponding number of surface drilling locations, which can beundesirable, particularly in offshore drilling operations. Methods,however, exist which allow non-vertical bores to be drilled permitting awide area to be accessed from a single surface drilling location. Suchmethods are commonly referred to as directional or controlled trajectorydrilling.

During directional drilling operations, a curved or deviated bore may bedrilled by placing a slight bend in the drilling assembly, referred toas a bent sub assembly, and orientating the bend in the requireddirection. For example, if the bend points upwards, the well bore willgain inclination angle. Likewise, if the bend points downwards, the wellwill drop angle and tend to return to a vertical plane. If the bend isused to point the drill bit left or right, the well bore will changedirection accordingly to the left or right.

Rotation of the drill bit is normally achieved by rotating the drillstring from surface level. When a bent sub assembly is present, therotation of the whole drill string negates the effect of the bent subassembly.

However, it is conventional to drive the drill bit during directionaldrilling using a downhole positive displacement mud motor which normallycomprises a long section of internally “twisted” pipe with a similarlytwisted rotor positioned therein. The flow of drilling fluid through thetwisted section will turn the rotor which is connected to the drill bitby a flexible steel rod which passes through the bent sub assembly. Inthis way, the drill bit is turned without the bent sub assembly rotatingand without the requirement for the whole drill pipe to be rotated fromthe surface.

However, when the bit makes contact with the rock face at the bottom ofthe bore, the torque generated by the mud motor has an equal andopposite reactive torque which will cause the drill string to twist orrotate back to surface level. The twist is normally significant andmakes control of the angle at which the bent sub points the drill bitdifficult to set and maintain.

Furthermore, when the drill string is not rotated, a situation known as“stick slip” occurs which can potentially damage the tooling. Stick slipoccurs because the weight applied to a stationary drill string toadvance a drill bit has to overcome static friction between the drillstring and the bore wall; the non-rotating string tends to stick in thebore, such that weight or force has to be applied to move the stringforward. The string will then often “unstick” suddenly, and slipforward, forcing the drill bit into the end of the bore and oftenstalling the mud motor. It is therefore preferred that the drill stringalso be rotated during all drilling operations such that a lower,dynamic friction has to be overcome, allowing for smoother drilling.

It is known to provide directional drilling while rotating the entiredrill assembly (“rotary directional drilling”), however, this requiresadditional and sometimes complicated and expensive downhole assembliesto maintain the bent sub in its desired orientation.

During directional drilling, it is essential that the direction in whichthe bent sub is pointing is known at all times, to ensure that the boreis being drilled in the correct direction and that adjustment to theorientation of the bent sub may be made as soon as an error is detected.In previously proposed rotary directional drilling systems, suchmonitoring is commonly achieved using dedicated complex electricalsystems which are provided in addition to the Measurement-While-Drilling(MWD) systems already provided within the bottom hole drilling assembly(BHA), thus increasing the complexity and expense of monitoringequipment which must be provided.

It is among the objectives of the embodiments of the present inventionto provide directional drilling apparatus which obviates, or at leastmitigates the aforementioned problems with the prior art.

SUMMARY OF INVENTION

According to a first aspect of the present invention, there is provideda drilling apparatus for drilling a deviated bore, said apparatuscomprising:

a tubular outer member having an offset and for rotatably supporting adrill bit, the member having gripping means for selectively engaging thewall of a bore to restrain the member against rotation;

an inner member within the outer member and for coupling to the drillbit at one end and to a drill string at another end;

wherein the apparatus has a first configuration in which the grippingmeans is retracted and the inner member is coupled to the outer membersuch that rotation of the drill string provides for correspondingrotation of the inner and outer members, and a second configuration inwhich the gripping means is extended and the inner member is rotatablerelative to the outer member such that the outer member is restrainedfrom rotation in the bore and rotation of the drill string provides forcorresponding rotation of the inner member and the drill bit.

Thus, with the apparatus in the first configuration, the offset of theouter tubular member may be rotated to a required orientation, whichorientation may then be maintained by reconfiguring the apparatus suchthat the outer member, including the offset, is then restrained fromfurther rotational motion. In the second configuration, the offset drillbit is rotated by the drill string, that is the offset drill bit isdriven from surface, thus obviating the need to provide a separatedownhole motor, and avoiding the difficulties that arise when attemptingto drill without rotation of the drill string.

Conveniently, the inner member may be moved in at least one of axiallyand rotatably relative to the outer member to reconfigure the apparatus.

Preferably, the inner member includes an elongate drive member, such asa drive rod, which extends through at least a portion of the outermember. An upper portion of the inner member may be adapted for couplingto the drill string, with a lower portion of the inner member adaptedfor coupling to the drill bit, the elongate drive member rotatablycoupling the lower portion of the inner member and the drill bit.

Preferably, the drive member is flexible, to accommodate differentrelative orientations of the offset. Preferably also, the drive memberis axially moveable relative to at least one of the lower portion of theinner member and the drill bit. The drive member and said at least oneof the lower portion of the inner member and the drill bit preferablydefine a cooperating profile to provide rotational coupling whilepermitting relative axial movement. For example, the drive member mayhave a hexagonal section, and the lower portion of the inner member orthe drill bit defines a cooperating hexagonal bore or bush.

Preferably, the inner member is coupled to the outer member byengagement of at least one pin mounted on one of the inner and outermembers, with at least one complementary profiled path in the other ofsaid inner and outer members. More preferably, the inner member iscoupled to the outer member by engagement of at least one pin on theouter surface of the inner member with at least one complementaryprofiled path or track on an inner surface of the outer member. In apreferred embodiment, a plurality of pins are provided on the innermember which respectively engage complementary profiled paths in theouter member. Thus, by moving the inner member relative to the outermember, the at least one pin may be moved within the correspondingprofiled path in order to reconfigure the drilling apparatus.

Preferably, the apparatus is arranged such that, in the firstconfiguration, the relative rotational orientation of the inner andouter members is known. This may be achieved by any appropriatemechanism, for example when pins or followers on one member engage pathsor tracks on the other member, these may be arranged such that the pinsor followers will only engage with a selected track or groove. In apreferred embodiment, one of the pins or followers may be longer thanthe others, and only a selected one of the paths or tracks may have alead-in which will accommodate the longer pin.

This preferred arrangement offers the advantage that, in the firstconfiguration, the relative orientation of the outer member, and itsoffset, to the inner member, and thus to the drill string, and theassociated bottom hole assembly (BHA), will always be the same. As theBHA conventionally includes MWD apparatus, this existing MWD apparatusmay be utilised to determine to orientation of the offset. Thus, theapparatus does not require the provision of dedicated MWD apparatus, orother orientation sensors, with a considerable saving in the costs ofproducing, using and maintaining the apparatus.

Preferably, in a third configuration, with weight applied to theapparatus, the gripping means is retracted and the inner member iscoupled to the outer member such that rotation of the drill stringprovides for corresponding rotation of the inner and outer members, andthe drill bit. The third configuration may thus be utilised for rotarydrilling with the offset rotating with the drill string and thus itsdirectional effect negated.

Preferably, the first configuration may be attained when the apparatusis lifted off bottom.

Preferably, the second configuration is attained with weight applied tothe apparatus.

Preferably, the apparatus is adapted to move between configurationssequentially, in response to the application and lifting of weight toand from the apparatus. In a preferred embodiment, the apparatus may becycled from the first configuration, to the second configuration, to thethird configuration, and then to the first configuration.

The gripping means may take any appropriate form. Preferably, thegripping means are weight actuated, that is the gripping means extendand retract in response to weight being applied to or lifted from theapparatus. The gripping means may comprise radially movable memberswhich engage movable cams or the like, but preferably comprise axiallyextending members which buckle or bow outwards on compression thereof.The members may carry ridges, teeth, or other profiles adapted to gripthe bore wail to prevent rotation but to permit axial sliding. In otherembodiments the gripping means may be fluid pressure actuated.Preferably, the gripping means is biased towards the retracted position.

Preferably, the apparatus includes a bearing between the inner and outermembers such that, in the second configuration, weight may be applied tothe drill bit from the drill string via the inner and outer memberswhile the inner member and drill bit rotate relative to the outermember.

According to a second aspect of the present invention, there is provideda drilling apparatus for drilling a deviated bore, said apparatuscomprising:

a tubular outer member having gripping means for selectively engagingthe wall of a bore to restrain the member against rotation and includingan offset portion for rotatably supporting a drill bit;

an inner member located within the outer member and for coupling to thedrill bit at one end and to a drill string at another end;

wherein the apparatus has a first configuration in which the grippingmeans is retracted and the inner member is coupled to the outer membersuch that rotation of the drill string provides for correspondingrotation of the inner and outer members, and a second configuration inwhich the gripping means is extended and the inner member is rotatablerelative to the outer member such that the outer member is restrainedfrom rotation in the bore and rotation of the drill string provides forcorresponding rotation of the inner member and the drill bit.

Conveniently, the inner member may be moved in at least one of axiallyand rotatably relative to the outer member to reconfigure the apparatus.

Preferably, the offset portion is rotatably mounted within a portion ofthe outer member and is rotatable relative thereto between a firstposition and a second position. Conveniently, the offset portion isaxially fixed relative to said portion of the outer member.

In a preferred embodiment, rotation of the offset portion between saidfirst and second positions occurs in response to axial movement of theinner member with respect to said portion of the outer member.

Conveniently, the offset portion has an axis of rotation disposed at anangle from an axis of rotation of said portion of the outer member.

Preferably, the drill bit is rotatably located relative to a lower endface of the offset portion, which lower end face is inclined from alateral axis of the offset portion such that, in the first rotationalposition, the inclination of the end face is negated by the angle ofoffset of the axis of rotation, resulting in the end face of the offsetportion being positioned substantially parallel to an end face of saidportion of the outer member. On the other hand, in the second rotationalposition, the effect of the inclination of the end face in combinationwith the angle of offset results in the end face of the offset portionbeing inclined relative to the end face of said portion of the outermember. Thus, when the offset portion is in a first rotational position,the drill bit will be coaxially aligned with said portion of the outermember, and when the offset portion is in a second position, the drillbit will be coaxially misaligned or offset.

Preferably, in the first configuration of the apparatus, the drill bitis coaxially aligned with said portion of the outer member, and in thesecond configuration, the drill bit is coaxially misaligned or offset.

Thus, with the apparatus in the first configuration, the outer membermay be rotated to locate the offset portion in a predeterminedorientation. The drill bit may then be offset by rotation of the offsetportion relative to said portion of the outer member, and the offsetmaintained by reconfiguring the apparatus such that the outer member,including the offset portion, is then restrained from further rotationalmotion. In the second configuration, the offset drill bit may be rotatedby the drill string, that is the offset drill bit is driven fromsurface, thus obviating the need to provide a separate downhole motor,and avoiding the difficulties that arise when attempting to drillwithout rotation of the drill string.

Preferably, rotation of the offset portion relative to said portion ofthe outer member is provided by at least one helical channel or tracklocated on the outer surface of the offset portion interacting with arespective rotationally fixed pin which is received within said at leastone channel. Thus axial movement of the rotationally fixed pin willcause rotational motion of the offset portion, which offset portion, asnoted above, is preferably fixed in an axial position relative to saidportion of the outer member. Preferably, a plurality of helical channelsare provided, and each interact with a respective pin.

The at least one channel or track may be formed in the surface of theoffset portion, or alternatively may be defined by fixing elongatemembers to the outer surface of the offset portion. The elongate membersmay be fixed in place, for example, by bolting, screwing or welding orthe like.

In a preferred embodiment, each rotationally fixed pin is provided on aninner surface of an intermediate tubular member which is located withinthe outer member, between the inner member and offset portion.Conveniently, the intermediate member is axially moveable androtationally fixed with respect to the outer member by, for example, alongitudinal sliding key and key-way arrangement. Thus, when theintermediate member is moved in an axial direction, the intermediatemember will move over the offset portion and the pins will engage arespective at least one channel or track to cause the offset portion torotate.

Preferably, the intermediate member is moved by corresponding axialmovement of the inner member relative to the outer member, thearrangement being such that movement of the inner member in a downwardsdirection will cause a bearing portion of the inner member to contact acorresponding bearing portion of the intermediate member, furtherdownward movement of the inner member causing the intermediate memberalso to move in a downwards direction. Conveniently, at least one of theinner member and intermediate member comprises a bearing race forlocation therebetween, in order to allow the inner member to rotaterelative to the intermediate member.

Conveniently, the intermediate member is biased in an upwards direction.

Preferably, when the intermediate member is moved downwards, the offsetportion is rotated to offset the drill bit. Conversely, when theintermediate member is moved in an upwards direction, the offset portionis rotated to coaxially align the drill bit with the outer member.

Preferably, the inner member is provided in combination with an elongatemember, such as a drive rod, which extends through at least a portion ofthe outer member. An upper portion of the inner member may be adaptedfor coupling to the drill string, with a lower portion of the innermember adapted for coupling to the drill bit, the elongate drive memberrotatably coupling the lower portion of the inner member and the drillbit.

Conveniently, the drive member is flexible, to accommodate differentrelative orientations of the offset.

Preferably also, the drive member is axially moveable relative to atleast one of the inner member and drill bit. The drive member and saidat least one of the inner member and drill bit preferably define acooperating profile to provide rotational coupling while permittingrelative axial movement. For example, the drive member may have ahexagonal section, and the inner member or drill bit defines acooperating hexagonal bore or bush.

Preferably, the inner member is coupled to the outer member byengagement of at least one pin mounted on one of the inner and outermembers, with at least one complementary profiled path in the other ofsaid inner and outer members. More preferably, the inner member iscoupled to the outer member by engagement of at least one pin on theouter surface of the inner member with at least one complementaryprofiled path or track on an inner surface of the outer member. In apreferred embodiment, a plurality of pins are provided on the innermember which respectively engage complementary profiled paths in theouter member. Thus, by moving the inner member relative to the outermember, the at least one pin may be moved within the correspondingprofiled path in order to reconfigure the drilling apparatus.Preferably, the apparatus is arranged such that, in the firstconfiguration, the relative rotational orientation of the inner memberand the outer member, including the offset portion, is known. This maybe achieved by any appropriate mechanism, for example when pins orfollowers on one member engage paths or tracks on the other member,these may be arranged such that the pins or followers will only engagewith a selected track or groove. In a preferred embodiment, one of thepins or followers may be longer than the others, and only a selected oneof the paths or tracks may have a lead-in which will accommodate thelonger pin.

This preferred arrangement offers the advantage that, in the firstconfiguration, the relative orientation of the outer member, includingthe offset portion, to the inner member, and thus to the drill string,and the associated bottom hole assembly (BHA), will always be the same.As the BHA conventionally includes MWD apparatus, this existing MWDapparatus may be utilised to determine the orientation of the offset.Thus, the apparatus does not require the provision of dedicated MWDapparatus, or other orientation sensors, with a considerable saving inthe costs of producing, using and maintaining the apparatus.

Preferably, in a third configuration, with weight applied to theapparatus, the gripping means is retracted and the drill bit iscoaxially aligned with said portion of the outer member, and the innermember is coupled to the outer member such that rotation of the drillstring provides for corresponding rotation of the inner and outermembers, and the drill bit. The third configuration may thus be utilisedfor fixed trajectory or non-deviated rotary drilling. This arrangementis favourable as during fixed trajectory drilling the drill bit iscoaxially aligned with the outer member, which eliminates the additionaldrilling forces and stresses which would otherwise be experienced by anoffset drill bit rotating about an offset axis.

Preferably, the first configuration may be attained when the apparatusis lifted off bottom.

Preferably, the second configuration is attained with weight applied tothe apparatus.

Preferably, the apparatus is adapted to move between configurationssequentially, in response to the application and lifting of weight toand from the apparatus. In a preferred embodiment, the apparatus may becycled from the first configuration, to the second configuration, to thethird configuration, and then to the first configuration.

The gripping means may take any appropriate form. Preferably, thegripping means are weight actuated, that is the gripping means extendand retract in response to weight being applied to or lifted from theapparatus. The gripping means may comprise radially movable memberswhich engage movable cams or the like, but preferably comprise axiallyextending members which buckle or bow outwards on compression thereof.The members may carry ridges, teeth, or other profiles adapted to gripthe bore wall to prevent rotation but to permit axial sliding. In otherembodiments the gripping means may be fluid pressure actuated.Preferably, the gripping means is biased towards the retracted position.

According to a third aspect of the present invention, there is provideda directional drilling apparatus comprising first and second cooperatingdrill bit support members for mounting a drill bit to a drill string,the members being arranged such that, in a first configuration, alateral axis of a drill bit supported by the members is substantiallyparallel with a lateral axis of a drill string on which the bit ismounted, and in a second configuration the drill bit axis is offset fromthe drill string axis.

Preferably, in the second configuration, the drill bit axis is offset atan angle from the drill string axis.

Conveniently, in the first configuration, a rotational axis of the drillbit is coaxially aligned with a rotational axis of the drill string, andin the second configuration, the rotational axis of the drill bit isoffset at an angle from the rotational axis of the drill string.

In a preferred embodiment, the directional drilling apparatus is movedfrom the first to second configurations by rotation of the second drillbit support member relative to the first member. Advantageously,rotation of the second member is achieved in response to axial movementof the first member.

It should be noted that the term drill string used above should beunderstood to include any tubular or rotational member commonly found ina well bore environment. For example, the directional drilling apparatusmay be utilised to mount a drill bit to drill pipe, drill collars, ortubular casing or liner or the like.

The directional drilling apparatus may be utilised in the manner asdescribed above with reference to the second aspect. Alternatively, thedirectional drilling apparatus may be used in conjunction with any otherappropriate drilling apparatus or Bottom Hole Assembly (BHA) for use indrilling a deviated bore.

The invention also relates to a method of directional drilling utilisingthe apparatus as described above with reference to the first to thirdaspects.

Those of skill in the art will also realise that some or all of thepreferred features described above may be utilised to advantage in otherforms of drilling apparatus, and are not restricted to use incombination with the abovementioned first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be described, by wayof example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic sectional view of drilling apparatus in accordancewith a preferred embodiment of a first aspect of the present invention,shown in a first configuration;

FIG. 2 shows the drilling apparatus of FIG. 1 in a second configuration;

FIG. 3 shows the drilling apparatus of FIG. 1 in a third configuration;

FIG. 4 is an enlarged perspective view of parts of an outer member andan inner member of the apparatus of FIG. 1, showing tracks defined bythe outer member and track following pins mounted on the inner member.

FIG. 5 is an enlarged view of one of the tracks provided in the outermember of FIG. 4;

FIG. 6 is a sectional view on line A-A of FIG. 2;

FIG. 7 is a sectional view on line B-B of FIG. 2;

FIG. 8 is a schematic sectional view of a drilling apparatus inaccordance with a preferred embodiment of a second aspect of the presentinvention, shown in a first configuration;

FIG. 9 shows the drilling apparatus of FIG. 8 in a second configuration;

FIG. 10 shows the drilling apparatus of FIG. 8 in a third configuration;

FIG. 11 is a perspective view of an offset portion of the apparatus ofFIG. 8;

FIG. 12 a shows a side cross-sectional view of the apparatus of FIG. 8;and

FIG. 12 b shows an enlarged front cross-sectional view on a line C-C ofFIG. 12 a.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIGS. 1 to 3 of the drawings which illustratea drilling apparatus 10 for drilling a deviated bore, in accordance withone embodiment of the present invention.

The apparatus comprises a tubular outer member 12 comprising an uppersleeve 14 defining a plurality of inner tracks 16, a tubular body 18carrying a plurality of spring grippers 20, and a leading bent sub 22defining an offset. Those of skill in the art will recognise that theoffset is exaggerated in the Figures; in practice, the offset istypically around 1 degree. The sub 22 provides a rotatable mounting fora drill bit 24, via bearing 26. The bit 24 is rotatably coupled to theend of a flexible hexagonal drive rod 28. The drive rod 28 extendsupwardly, through the bent sub 22 and body 18, and is rotatably coupledto an inner member 32, the lower end of the member 32 being locatedwithin the outer upper sleeve 14 and provided with studs 33 for engagingrespective tracks 16 in the sleeve 14. The upper end of the member 32 iscoupled to the drill string (not shown).

In a first configuration, as illustrated in FIG. 1 of the drawings, thegrippers 20 are radially retracted, and in use will describe a diameterless than the inner diameter of the bore being drilled. The outer andinner members 12, 32 are rotatably coupled, such that rotation of thedrill string from surface causes the entire apparatus 10 to rotate inunison. As will be described, the relative orientation of the coupledmembers 12, 32 is known, such that by monitoring the output of the MWDapparatus provided in the bottom hole assembly (BHA) of the drill stringabove the apparatus 10, which MWD apparatus will indicate, among otherthings, the orientation of the BHA, the orientation of the bent sub 22may be determined. Thus, by rotating the string from surface, a desiredand readily determined bent sub orientation may be achieved.

Once the bent sub 22 has been orientated as desired, the apparatus 10 isreconfigured, to the second configuration, as illustrated in FIG. 2, toretain the selected orientation and to drill in the resulting selecteddirection. As will subsequently be described in greater detail,reconfiguring the apparatus 10 radially extends the grippers 20 toengage the surrounding wall, while disengaging the outer and innermembers 12, 32 such that the inner member 32 may be rotated in the borewhile the outer member 12 does not rotate. The orientation of the bentsub 22 is therefore retained while the drill bit 24 may be rotated fromsurface, via the inner member 32.

For drilling straight ahead, the apparatus 10 is arranged in a thirdconfiguration, as illustrated in FIG. 3 of the drawings. In thisconfiguration, the grippers 20 are retracted and the outer and innermembers 12, 32 are rotationally coupled. Thus, rotation of the bit 24 isaccompanied by rotation of the outer member 12, including the bent sub22, such that the effect of the bent sub 22 is negated.

The construction and operation of the apparatus will now be described ingreater detail, with reference also to FIGS. 4 to 7 of the drawings.

Reconfiguring the apparatus 10 is achieved simply by the sequentialapplication of weight to the apparatus 10 and then lifting the bit 24off bottom, such that a tension is applied to the apparatus 10.

FIGS. 4 and 5 illustrate the tracks 16 which are machined into the innerface of the upper sleeve 14, and the studs 33 which are arranged to movein an anti-clockwise direction around the tracks 16 as the apparatus iscycled between configurations. With reference to FIG. 5, the studpositions 33 a, 33 b and 33 c correspond to the first, second and thirdconfigurations shown in FIGS. 1, 2 and 3, respectively.

One of the six studs 33 f is longer than the others, as is visible inFIG. 6 of the drawings which is a sectional view of FIG. 2 through A-A .This stud 33 f cooperates with a deeper cut track 16 f (FIG. 4) having aflared lead-in 40, such that the longer stud 33 f can only be located inthe deeper track. Thus, when the outer and inner members 12, 32 arerotatably coupled, the relative rotational positions of the members 12,32 are known.

Reference is now made in particular to FIG. 7 of the drawings, which isa sectional view through B-B of FIG. 2 showing the spring grippers 20 intheir extended configuration, extending radially beyond gripper locatingslots 42 in the body 18. The grippers 20 are in the form of axiallyextending rectangular bands and each carries an axial ridge 44 to gripthe bore wall to prevent rotation while permitting axial movement. FromFIG. 2 it will be noted that the lower end of each gripper 20 isretained in a slot 46 in the body 18, while the upper end of eachgripper 20 is attached too a bearing race 48 located between the upperend of the body 18 and the lower end of upper sleeve 14.

When the apparatus 10 is in the second configuration, the lower end ofthe inner member 32 contacts and moves the bearing race 48 down towardsthe upper end of the body 18, causing the grippers 20 to bow outwards toengage and grip the bore wall. In the first and third positions, thebearing race 48 is free to move upwards under the return force of thegripper bands 20.

For normal drilling of a bore straight ahead, the apparatus 10 ismaintained in the second configuration (FIG. 2), with the studs 33 inthe position 33 b (FIG. 5). Weight applied from surface, or from themass of the drill string above the apparatus, is transmitted to the bit24 from the inner member 32 to the outer sleeve 14 via the studs 33, andthrough the body 18 and the bent sub 22.

The inner member 32 is prevented from coming into contact with thebearing race 48 as axial movement of the member 32 is restrained by thestuds 33 engaging with the tracks 16, such that the grippers 20 remainretracted. Thus, the apparatus 10 rotates as one with the drill string,the rotation of the bent sub 22 negating the effect of the offset.

If it is desired to deviate the bore in a particular direction, rotationof the string is stopped, and the string lifted from bottom, such thatstuds 33 travel up the respective tracks 16 to position 33 a (FIG. 5),the inner member 32 sliding upwardly over the drive rod 28. Theapparatus 10 is now in the first configuration as shown in FIG. 1. Theinner member 32 remains rotatably coupled to the outer sleeve 14, suchthat rotation of the string causes the apparatus, including the bent sub22, to rotate in the bore.

By monitoring the MWD of the BHA, the bent sub 22 may be postponed in adesired orientation, to achieve the desired deviation of the bore.

If weight is then applied to the apparatus 10, the studs 33 move downthe tracks 16 beyond the lower ends of the tracks 16, to position 33 b,such that the apparatus is in the second configuration (FIG. 2).

In this configuration, the studs 33 are clear of the tracks 16 and thusthe inner member 32 may rotate without causing corresponding rotation ofthe outer sleeve 14, drive rod 28 transferring rotation from the member32 to the drill bit 24. The lower end of the inner member 32 engages thebearing race 48, causing the grippers 20 to buckle outwardly intocontact with the bore wall, preventing the outer member 12 fromrotating.

Thus, in this configuration, when the drill string is rotated, the outermember 12 does not rotate, while the bit 24 is rotated and advances thebore in the direction of selected orientation of the bent sub 22.

When the orientation of the BHA, and thus the bore, as measured by theMWD apparatus, has changed to that desired by the driller, rotation ofthe drill string is halted. The drill string is then lifted, and thenweight applied once more to locate the studs 33 in the position 33 c.The bore may then be drilled on, maintained to previously attained boreorientation.

Reference is now made to FIGS. 8 to 10 of the drawings in which there isshown a drilling apparatus 100 for drilling a deviated bore, inaccordance with an alternative embodiment of the present invention. Itshould be noted that the apparatus 100 is similar to that apparatus 10shown in FIGS. 1 to 7, and as such like components share the samereference numerals, preceded by a “1”.

The apparatus 100 comprises a tubular outer member 112 having an upperportion defining a number of tracks 116 and including a plurality ofspring grippers 120. Rotatably mounted within a lower portion of theouter member 112 is an offset portion 150, which portion 150 has an axisof rotation disposed at an angle from an axis of rotation of the outermember 112. The offset portion 150 is axially fixed relative to theouter member by way of an annular collar 152 mounted on the outersurface of the offset portion 150 engaging an annular recess 154 in theinner surface of the outer member 112.

A drill bit 124 is rotatably located on an end face 156 of the offsetportion 150 via bearing 126. The face 156 upon which the drill bit 124is located is inclined from a lateral axis of the offset portion 150,which feature is used in offsetting the drill bit 124 to effectdirectional drilling, as will be described in more detail below.

The drill bit 126 is rotatably coupled to the end of a flexible driverod 128 which extends upwardly through the outer member 112 and isrotatably coupled to an inner member 132. The lower end of the member132 is located within the upper portion of the outer member 112 and isprovided with studs 133 for engaging respective tracks 116 in the outermember 112. The interaction of the pins 133 with the tracks 116 allowsthe apparatus 100 to be reconfigured in the same manner as describedabove with reference to FIGS. 4 to 6. The upper end of the inner member132 is coupled to the drill string (not shown).

The apparatus further comprises an intermediate tubular member 158located between the inner member 132 and the offset portion 150. Theintermediate tubular member 158 is axially moveable and rotationallyfixed with respect to the outer member 112 by engagement ofdiametrically opposed key portions 160 on the intermediate member 158with respective longitudinal key-ways 162. In use, axial movement of theintermediate member 158 is translated to rotational movement of theoffset portion 150 in order to orientate the drill bit 124 in therequired direction. Axial movement of the intermediate tubular member158 is translated to rotational movement of the offset portion 150 byinteraction of a plurality of pins 164 mounted on the inner surface ofthe intermediate member 158 with respective helical tracks 166 in theouter surface of the offset portion 150. The form of the tracks 166 ismore clearly shown in FIG. 11, which is a perspective view of the offsetportion 150. Also shown in FIG. 11 is the annular collar 152 which, inconjunction with the annular recess 154 in the outer member 112, shownin FIG. 8 to 10, prevents the offset portion 150 from moving in an axialdirection with respect to the outer member 112. A clearer view of theinteraction between the outer and intermediate members 112, 158 and theoffset portion 150.is shown in FIGS. 12 a and b, with a correspondingdescription given hereinafter.

The intermediate tubular member 158 moves the offset portion 150 betweenfirst and second rotational positions. In the embodiment shown, theoffset portion 150 is moved from the first to the second position bymovement of the intermediate member 158 in a downwards direction, andvice versa. In the first position, shown in FIG. 8, the inclination ofthe end face 156 of the offset portion 150 is negated by the offset ofthe axis of rotation, resulting in the end face 156 being positionedsubstantially parallel to an end face of the outer member 112, and thedrill bit 124 being coaxially aligned with the outer member 112. In thesecond position, shown in FIG. 9, the effect of the inclination of theend face 156 in combination with the angle of offset results in the endface 156 being inclined relative to the end face of the outer member112. Thus, when the offset portion 150 is in the second position, thedrill bit 124 is coaxially misaligned or offset.

In a first configuration, as illustrated in FIG. 8 of the drawings, thegrippers 120 are radially retracted and the outer and inner members 112,132 are rotatably coupled, such that rotation of the drill string fromsurface causes the entire apparatus 100 to rotate in unison. Asdescribed above with reference to the first embodiment of the invention,it is possible to determine the relative orientation of the rotarycoupled members 112, 132 such that a desired and readily determinedinitial orientation of the offset portion 150 may be achieved. It shouldbe noted that in the first configuration, no weight is applied to theapparatus 100 from the drill string.

Once the desired initial orientation of the offset member 150 isachieved, the apparatus 100 is reconfigured to a second configuration,shown in FIG. 9, wherein the drill bit 124 is coaxially misaligned, to apredetermined extent and in a predetermined direction by rotation of theoffset portion 150 relative to the outer member 112, and the grippers120 are radially extended to engage the surrounding wall to preventrotation of the outer member 112, and thus maintain the desired, finaloffset of the drill bit 124. Additionally, in the second configuration,the inner member 132 is disengaged from the outer member 112 such thatthe inner member 132 may be rotated in the bore while the outer member112 does not rotate. The orientation of the drill bit 124 is thereforeretained while the drill bit 124 may be rotated from surface.

As noted hereinbefore, the offset member 150 is rotated to orientate thedrill bit 124 by corresponding axial movement of the intermediate member158. Axial movement of the intermediate member 158 is achieved inresponse to axial movement of the inner member 132, the arrangementbeing such that movement of the inner member 132 in a downwardsdirection will cause a bearing portion of the inner member 132 tocontact a corresponding bearing portion of the intermediate member 158,further downward movement of the inner member 132 causing theintermediate member 158 also to move in a downwards direction.Positioned on the intermediate member 158 is a bearing race 168 whichallows the inner member 132 to rotate relative to the intermediatemember 158 when the apparatus 100 is in the second configuration andalso provides a weight transfer point from the drill string to the drillbit 124.

If fixed trajectory or non-deviated drilling is required, the apparatus100 may be reconfigured into a third configuration, as shown in FIG. 10of the drawings. In this configuration, the grippers 120 are retractedand the outer and inner members 112, 132 are rotationally coupled, andweight is applied to the apparatus 100 by the drilling string via pins133 on the inner member 132. The offset portion 150 is located in itsfirst position by movement of the intermediate member 158 in an upwardsdirection such that the drill bit 124 is coaxially aligned with theouter member 112. The intermediate member 158 is biased towards movementin an upwards direction under the return force of the gripper bands 120.Thus, when the inner member 132 is lifted from the bearing 168 of theintermediate member 158, the intermediate member 158 will move in anupwards direction due to the retraction of the grippers 120. It shouldbe noted that the gripper bands 120 of the current embodiment aresimilar to those as described with reference to FIG. 7, and thus nofurther description will be given. Thus, by action of the intermediatemember 158, the offset portion 150 is biased towards its firstrotational position wherein the drill bit 124 is coaxially aligned. Thearrangement of having the drill bit 124 coaxially aligned in the thirdconfiguration of the apparatus during fixed trajectory drilling isparticularly advantageous as the additional drilling forces and stresseson the apparatus which would otherwise be experienced by use of anoffset drill bit are eliminated.

A more detailed view of the interaction of the offset portion 150,intermediate member 158 and outer member 112 is shown in FIGS. 12 a andb, which respectively show an enlarged side view and correspondingcross-sectional view, through C-C of FIG. 12 a, of the apparatus 100. Asdiscussed above, the intermediate member 158 is axially moveable androtationally fixed with respect to the outer member 112 by diametricallydisposed, longitudinal sliding key 160 and key-way 162 arrangements. Theintermediate member 158 comprises a plurality of pins 164 which engagerespective helical tracks 166 in the offset portion 150 to effectrotational movement thereof, and therefore position the drill bit 124 inits desired orientation.

It will thus be appreciated that the apparatuses 10, 100 providerelatively simple and robust arrangements for permitting rotarydirectional drilling.

It will of course be appreciated by those of skill in the art that theabove described example is merely exemplary of the present invention,and that various modifications and improvements may be made thereto,without departing from the scope of the invention. For example, thedrive rod 28 may be hollow, to allow objects and tools, such as loggingtools, to be run in through the apparatus. In certain embodiments, sucha hollow drive rod may be utilised together with a drill bit having aremovable portion, to permit “through-the-bit-logging”. Such anarrangement is described in U.S. Pat. No. 6,269,891 which relates to asystem and method of drilling and logging an earth formation.

1. A drilling apparatus for drilling a deviated bore, said apparatuscomprising: a tubular outer member having an offset and for rotatablysupporting a drill bit, the member having gripping means for selectivelyengaging the wall of a bore to restrain the member against rotation; aninner member within the outer member and for coupling to the drill bitat one end and to a drill string at another end; wherein the apparatushas a first configuration in which the gripping means is retracted andthe inner member is coupled to the outer member such that rotation ofthe drill string provides for corresponding rotation of the inner andouter members, and a second configuration in which the gripping means isextended and the inner member is rotatable relative to the outer membersuch that the outer member is restrained from rotation in the bore androtation of the drill string provides for corresponding rotation of theinner member and the drill bit.
 2. A drilling apparatus as claimed inclaim 1, wherein the inner member is at least one of axially moveableand rotatably moveable relative to the outer member, to reconfigure theapparatus.
 3. A drilling apparatus as claimed in claim 1, wherein theinner member includes an elongate drive member which extends through atleast a portion of the outer member.
 4. A drilling apparatus as claimedin claim 3, wherein the elongate drive member is a drive rod.
 5. Adrilling apparatus as claimed in claim 3, wherein an upper portion ofthe inner member is adapted for coupling to the drill string, with alower portion of the inner member adapted for coupling to the drill bit,the elongate drive member rotatably coupling the upper and lowerportions.
 6. A drilling apparatus as claimed in claim 3 wherein thedrive member is flexible, to accommodate different relative orientationsof the offset.
 7. A drilling apparatus as claimed in claim 3, whereinthe drive member is axially moveable relative to at least one of thelower portion of the inner member and the drill bit.
 8. A drillingapparatus as claimed in claim 3, wherein the drive member and at leastone of the lower portion of the inner member and the drill bit define acooperating profile to provide rotational coupling while permittingrelative axial movement.
 9. A drilling apparatus as claimed in claim 8,wherein the drive member has a hexagonal section, and the lower portionof the inner member or the drill bit defines a cooperating hexagonalbore.
 10. A drilling apparatus as claimed in claim 1, wherein the innermember is coupled to the outer member by engagement of at least one pinmounted on one of the inner and outer members, with at least onecomplementary profiled track in the other of said inner and outermembers.
 11. A drilling apparatus as claimed in claim 1, wherein theinner member is coupled to the outer member by engagement of at leastone pin on the outer surface of the inner member with at least onecomplementary profiled track on an inner surface of the outer member.12. A drilling apparatus as claimed in claim 11, wherein a plurality ofpins are provided on the inner member which respectively engagecomplementary profiled tracks in the outer member.
 13. A drillingapparatus as claimed in claim 1, wherein the apparatus is arranged suchthat, in the first configuration, the relative rotational orientation ofthe inner and outer members is predetermined.
 14. A drilling apparatusas claimed in claim 10, wherein when pins on one member engage profiledtracks on the other member, the pins and profiled tracks being arrangedsuch that the pins will only engage with a selected respective profiledtrack.
 15. A drilling apparatus as claimed in claim 10, wherein one ofthe pins is longer than the others, and only a selected one of theprofiled tracks has a lead-in which will accommodate the longer pin. 16.A drilling apparatus as claimed in claim 1, wherein the apparatus has athird configuration, in which third configuration, with weight appliedto the apparatus, the gripping means is retracted and the inner memberis coupled to the outer member such that rotation of the drill stringprovides for corresponding rotation of the inner and outer members, andthe drill bit.
 17. A drilling apparatus as claimed in claim 16, whereinthe apparatus in a third configuration may be utilized for rotarydrilling with the offset rotating with the drill string and thus itsdirectional effect negated.
 18. A drilling apparatus as claimed in claim1, wherein the first configuration may be attained when the apparatus islifted off bottom.
 19. A drilling apparatus as claimed in claim 1,wherein the second configuration is attained with weight applied to theapparatus.
 20. A drilling apparatus as claimed in claim 1, wherein theapparatus is adapted to move between configurations sequentially, inresponse to the application and lifting of weight to and from theapparatus.
 21. A drilling apparatus as claimed in claim 20, wherein theapparatus has a third configuration, in which third configuration, withweight applied to the apparatus, the gripping means is retracted and theinner member is coupled to the outer member such that rotation of thedrill string provides for corresponding rotation of the inner and outermembers, and the drill bit, and wherein the apparatus is cycled from thefirst configuration, to the second configuration, to the thirdconfiguration, and then to the first configuration.
 22. A drillingapparatus as claimed in claim 1, wherein the gripping means are weightactuated such that the gripping means is extended and retracted inresponse to weight being applied to or lifted from the apparatus.
 23. Adrilling apparatus as claimed in claim 1, wherein the gripping meanscomprises axially extending members which buckle outwards on compressionthereof.
 24. A drilling apparatus as claimed in claim 23, wherein themembers carry profiles adapted to grip the bore wall to prevent rotationbut to permit axial sliding.
 25. A drilling apparatus as claimed inclaim 24, wherein the profiles are ridges.
 26. A drilling apparatus asclaimed in claim 1 wherein the gripping means is biased towards theretracted position.
 27. A drilling apparatus as claimed in claim 1,wherein the apparatus includes a bearing between the inner and outermembers such that, in the second configuration, weight may be applied tothe drill bit from the drill string via the inner and outer memberswhile the inner member and drill bit rotate relative to the outermember.
 28. A drilling apparatus as claimed in claim 1, wherein theinner member is hollow.
 29. A drilling apparatus as claimed in claim 28,in combination with a logging tool adapted to be run-in through theinner member.
 30. A drilling apparatus for drilling a deviated bore,said apparatus comprising: a tubular outer member having gripping meansfor selectively engaging the wall of a bore to restrain the memberagainst rotation and including an offset portion for rotatablysupporting a drill bit; an inner member located within the outer memberand for coupling to the drill bit at one end and to a drill string atanother end; wherein the apparatus has a first configuration in whichthe gripping means is retracted and the inner member is coupled to theouter member such that rotation of the drill string provides forcorresponding rotation of the inner and outer members, and a secondconfiguration in which the gripping means is extended and the innermember is rotatable relative to the outer member such that the outermember is restrained from rotation in the bore and rotation of the drillstring provides for corresponding rotation of the inner member and thedrill bit.
 31. A drilling apparatus as claimed in claim 30, wherein theinner member is moveable in at least one of axially and rotatablyrelative to the outer member to reconfigure the apparatus.
 32. Adrilling apparatus as claimed in claim 30, wherein the offset portion isrotatably mounted within a portion of the outer member and is rotatablerelative thereto between a first position and a second position.
 33. Adrilling apparatus as claimed in claim 32, wherein the offset portion isaxially fixed relative to said portion of the outer member.
 34. Adrilling apparatus as claimed in claim 31, wherein rotation of theoffset portion between said first and second positions occurs inresponse to axial movement of the inner member with respect to saidportion of the outer member.
 35. A drilling apparatus as claimed inclaim 30, wherein the offset portion has an axis of rotation disposed atan angle from an axis of rotation of said portion of the outer member.36. A drilling apparatus as claimed in claim 32, wherein the drill bitis rotatably located relative to a lower end face of the offset portion,which lower end face is inclined from a lateral axis of the offsetportion such that, in the first rotational position, the inclination ofthe end face is negated by the angle of offset of the axis of rotation,resulting in the end face of the offset portion being positionedsubstantially parallel to an end face of said portion of the outermember.
 37. A drilling apparatus as claimed in claim 36, wherein, in thesecond rotational position, the effect of the inclination of the endface in combination with the angle of offset of the rotational axis ofthe offset portion results in the end face of the offset portion beinginclined relative to the end face of said portion of the outer member.38. A drilling apparatus as claimed in claim 32, wherein, when theoffset portion is in a first rotational position, the drill bit will becoaxially aligned with said portion of the outer member, and when theoffset portion is in a second position, the drill bit will be coaxiallymisaligned.
 39. A drilling apparatus as claimed in claim 32, wherein, inthe first configuration of the apparatus, the drill bit is coaxiallyaligned with said portion of the outer member, and in the secondconfiguration, the drill bit is coaxially misaligned.
 40. A drillingapparatus as claimed in claim 32, wherein rotation of the offset portionrelative to said portion of the outer member is provided by at least onehelical track located on the outer surface of the offset portioninteracting with a respective rotationally fixed pin which is receivedwithin said at least one channel.
 41. A drilling apparatus as claimed inclaim 40, wherein a plurality of helical tracks are provided, and eachinteract with a respective pin.
 42. A drilling apparatus as claimed inclaim 40, wherein the at least one helical track is formed in thesurface of the offset portion.
 43. A drilling apparatus as claimed inclaim 40, wherein the at least one helical track is defined by fixingelongate members to the outer surface of the offset portion.
 44. Adrilling apparatus as claimed in claim 40, wherein each rotationallyfixed pin is provided on an inner surface of an intermediate tubularmember which is located within the outer member, between the innermember and offset portion.
 45. A drilling apparatus as claimed in claim44, wherein the intermediate member is axially moveable and rotationallyfixed with respect to the outer member.
 46. A drilling apparatus asclaimed in claim 45, wherein the intermediate member is axially moveableand rotationally fixed with respect to the outer member by alongitudinal sliding key and key-way arrangement.
 47. A drillingapparatus as claimed in claim 45, wherein the intermediate member ismoved axially by corresponding axial movement of the inner memberrelative to the outer member, the arrangement being such that movementof the inner member in a downwards direction will cause a bearingportion of the inner member to contact a corresponding bearing portionof the intermediate member, further downward movement of the innermember causing the intermediate member also to move in a downwardsdirection.
 48. A drilling apparatus as claimed in claim 44, wherein atleast one of the inner member and intermediate member comprises abearing race for location therebetween, in order to allow the innermember to rotate relative to the intermediate member.
 49. A drillingapparatus as claimed in claim 44, wherein the intermediate member isbiased in an upwards direction.
 50. A drilling apparatus as claimed inclaim 47, wherein, when the intermediate member is moved downwards, theoffset portion is rotated to misalign the drill bit.
 51. A drillingapparatus as claimed in claim 47, wherein, when the intermediate memberis moved in an upwards direction, the offset portion is rotated tocoaxially align the drill bit with the outer member.
 52. A drillingapparatus as claimed in claim 30, wherein the inner member includes anelongate drive member which extends through at least a portion of theouter member.
 53. A drilling apparatus as claimed in claim 52, whereinthe elongate drive member is a drive rod.
 54. A drilling apparatus asclaimed in claim 52, wherein an upper portion of the inner member isadapted for coupling to the drill string, with a lower portion of theinner member adapted for coupling to the drill bit, the elongate drivemember rotatably coupling the lower portion of the inner member and thedrill bit.
 55. A drilling apparatus as claimed in claim 52, wherein thedrive member is flexible, to accommodate different relative orientationsof the offset.
 56. A drilling apparatus as claimed in claim 52, whereinthe drive member is axially moveable relative to at least one of thelower portion of the inner member and drill bit.
 57. A drillingapparatus as claimed in claim 52, wherein the drive member and at leastone of the inner member and drill bit define a cooperating profile toprovide rotational coupling while permitting relative axial movement.58. A drilling apparatus as claimed in claim 57, wherein the drivemember has a hexagonal section, and the inner member or drill bitdefines a cooperating hexagonal bore.
 59. A drilling apparatus asclaimed in claim 30, wherein the inner member is coupled to the outermember by engagement of at least one pin mounted on one of the inner andouter members, with at least one complementary profiled path in theother of said inner and outer members.
 60. A drilling apparatus asclaimed in claim 30, wherein, wherein the inner member is coupled to theouter member by engagement of at least one pin on the outer surface ofthe inner member with at least one complementary profiled path or trackon an inner surface of the outer member.
 61. A drilling apparatus asclaimed in claim 60, wherein a plurality of pins are provided on theinner member which respectively engage complementary profiled paths inthe outer member.
 62. A drilling apparatus as claimed in claim 30,wherein the apparatus is arranged such that in a first configuration,the relative rotational orientation of the inner and outer members ispredetermined.
 63. A drilling apparatus as claimed in claim 59, whereinwhen pins on one member engage profiled tracks on the other member, thepins and profiled tracks being arranged such that the pins will onlyengage with a selected respective profiled track.
 64. A drillingapparatus as claimed in claim 59, wherein one of the pins is longer thanthe others, and only a selected one of the profiled tracks has a lead-inwhich will accommodate the longer pin.
 65. A drilling apparatus asclaimed in claim 30, wherein the apparatus has a third configuration, inwhich third configuration, with weight applied to the apparatus, thegripping means is retracted and the drill bit is coaxially aligned withsaid portion of the outer member, and the inner member is coupled to theouter member such that rotation of the drill string provides forcorresponding rotation of the inner and outer members, and the drillbit.
 66. A drilling apparatus as claimed in claim 65, wherein theapparatus in a third configuration is utilized for fixed trajectoryrotary drilling.
 67. A drilling apparatus as claimed in claim 30,wherein the first configuration may be attained when the apparatus islifted off bottom.
 68. A drilling apparatus as claimed in claim 30,wherein the second configuration is attained with weight applied to theapparatus.
 69. A drilling apparatus as claimed in claim 30, wherein theapparatus is adapted to move between configurations sequentially, inresponse to the application and lifting of weight to and from theapparatus.
 70. A drilling apparatus as claimed in claim 69, wherein theapparatus has a third configuration, in which third configuration, withweight applied to the apparatus, the gripping means is retracted and thedrill bit is coaxially aligned with said portion of the outer member,and the inner member is coupled to the outer member such that rotationof the drill string provides for corresponding rotation of the inner andouter members, and the drill bit, and wherein the apparatus is cycledfrom the first configuration, to the second configuration, to the thirdconfiguration, and then to the first configuration.
 71. A drillingapparatus as claimed in claim 30, wherein the gripping means are weightactuated such that the gripping means is extended and retract inresponse to weight being applied to or lifted from the apparatus.
 72. Adrilling apparatus as claimed in claim 30, wherein the gripping meanscomprises axially extending members which buckle outwards on compressionthereof.
 73. A drilling apparatus as claimed in claim 72, wherein themembers carry profiles adapted to grip the bore wall to prevent rotationbut to permit axial sliding.
 74. A drilling apparatus as claimed inclaim 30, wherein the gripping means is biased towards the retractedposition.
 75. A directional drilling apparatus comprising first andsecond cooperating drill bit support members for mounting a drill bit toa drill string, the members being arranged such that, in a firstconfiguration, a lateral axis of a drill bit supported by the members issubstantially parallel with a lateral axis of a drill string on whichthe bit is mounted, and in a second configuration the drill bit axis isoffset from the drill string axis.
 76. A directional drilling apparatusas claimed in claim 75, wherein, in the second configuration, the drillbit axis is offset at an angle from the drill string axis.
 77. Adirectional drilling apparatus as claimed in claim 75, wherein, in thefirst configuration, a rotational axis of the drill bit is coaxiallyaligned with a rotational axis of the drill string, and in the secondconfiguration, the rotational axis of the drill bit is offset at anangle from the rotational axis of the drill string.
 78. A directionaldrilling apparatus as claimed in claim 75, wherein the apparatus ismoved from the first to second configurations in response to rotation ofthe second drill bit support member.
 79. A directional drillingapparatus as claimed in claim 78, wherein rotation of the second memberis achieved in response to axial movement of the first member.
 80. Adrilling apparatus substantially as described herein and as shown in theaccompanying representations.
 81. A method of directional drillingutilizing the apparatus as described in claim
 1. 82. A method ofdirectional drilling utilizing the apparatus as described in claim 30.83. A method of directional drilling utilizing the apparatus asdescribed in claim 75.